论文标题

分层培养基中的湍流加热

Turbulent Heating in a Stratified Medium

论文作者

Wang, Chaoran, Oh, S. Peng, Ruszkowski, M.

论文摘要

有大量证据表明,星系簇中广泛的亚音速湍流,最著名的是{\ it hitomi}。通常通过直接耗散和实现湍流热扩散来挑选湍流以抵消簇核中辐射损失。但是,在分层的介质中,浮力反对径向运动,使湍流各向异性。可以通过Froude Number $ {\ rm fr} $量化这一点,该$随着分层的增加而在集群中降低。我们利用MHD湍流利用类比,以表明波动扰动的相互作用会增加级联时的时间并降低耗散率$ε\ propto {\ rm fr} $。同等地,对于给定的能量注入/耗散率$ε$,与Kolmogorov量表相比,动荡的速度$ u $必须更高。高分辨率的流体动力模拟与$ε\ propto {\ rm fr} $缩放显示出了极好的一致性,该缩放设置为$ {\ rm fr} <0.1 $。我们还比较了先前预测的量表的湍流扩散系数$ d \ propto {\ rm fr}^2 $,并找到出色的协议,以$ {\ rm fr} <1 $。但是,我们发现不同的归一化,对应于更强的扩散抑制,而不是一个数量级。我们的结果表明,与湍流耗散相比,分层在较大的径向范围内更严重地抑制了湍流扩散。因此,后者潜在地主导。此外,与以前的型号相比,这种转移意味着抵消冷却所需的湍流速度明显更高。这些结果可能与湍流金属扩散(同样受到抑制)和行星大气有关。

There is considerable evidence for widespread subsonic turbulence in galaxy clusters, most notably from {\it Hitomi}. Turbulence is often invoked to offset radiative losses in cluster cores, both by direct dissipation and by enabling turbulent heat diffusion. However, in a stratified medium, buoyancy forces oppose radial motions, making turbulence anisotropic. This can be quantified via the Froude number ${\rm Fr}$, which decreases inward in clusters as stratification increases. We exploit analogies with MHD turbulence to show that wave-turbulence interactions increase cascade times and reduces dissipation rates $ε\propto {\rm Fr}$. Equivalently, for a given energy injection/dissipation rate $ε$, turbulent velocities $u$ must be higher compared to Kolmogorov scalings. High resolution hydrodynamic simulations show excellent agreement with the $ε\propto {\rm Fr}$ scaling, which sets in for ${\rm Fr} < 0.1$. We also compare previously predicted scalings for the turbulent diffusion coefficient $D \propto {\rm Fr}^2$ and find excellent agreement, for ${\rm Fr} < 1$. However, we find a different normalization, corresponding to stronger diffusive suppression by more than an order of magnitude. Our results imply that turbulent diffusion is more heavily suppressed by stratification, over a much wider radial range, than turbulent dissipation. Thus, the latter potentially dominates. Furthermore, this shift implies significantly higher turbulent velocities required to offset cooling, compared to previous models. These results are potentially relevant to turbulent metal diffusion (which is likewise suppressed), and to planetary atmospheres.

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